1. Field of the Invention
The present invention relates to a micro electro mechanical system (MEMS) microphone, and more particularly, to a MEMS microphone in which a back chamber space for a MEMS chip may be secured in order to obtain improved sound characteristics.
2. Description of the Related Art
A microphone is necessarily used in a mobile communication terminal. A traditional type condenser microphone includes a pair elements formed of a diaphragm and a back plate for forming a capacitance C that changes in correspondence with sound pressure and a junction field effect transistor (JFET) for buffering output signals.
Such a traditional type condenser microphone is completely formed as a single assembly by inserting a diaphragm, a spacer ring, an insulation ring, a back plate, and an electric current application ring into a single case in the stated order, inserting a PCB, on which circuit devices are mounted, into the case, and bending an end of the case toward the PCB.
Recently, a semiconductor fabrication technique using micromachining methods has been used for improving the integration of fine devices. By using this technique, a so-called micro electro mechanical system (MEMS), μm-sized ultra-small sensors, actuators, and electro-mechanical structures may be fabricated by using micromachining methods, and more particularly, integrated circuit methods, in a semiconductor fabrication process.
In a MEMS chip microphone fabricated by using such micromachining methods, traditional microphone components, such as a diaphragm, a spacer ring, an insulation ring, a back plate, and an electric current application ring may be miniaturized, multi-functionalized, and densely integrated via ultra-high precision fabrication methods for improved stability and reliability.
FIG. 1 is a schematic sectional view of a conventional MEMS microphone 100 having a MEMS chip 120. The MEMS microphone 100 includes a printed circuit board (PCB) 110, the MEMS chip 120 mounted on the PCB 110, an application specific integrated circuit (ASIC) chip 130, which is also referred to as an amplifier, and a case 150 in which sound holes 140 are formed.
In FIG. 1, reference numeral 126 is a space formed inside a MEMS chip. In case of a MEMS microphone in which sound holes are formed in a case as described above, the inner-MEMS space 126 is a back chamber. A back chamber is a space for circulating air generated by oscillation of a diaphragm arranged at the MEMS chip for preventing formation of an acoustic resistance. In other words, the back chamber is a space on the opposite side of a side of a diaphragm where external sound is introduced. When the size of the back chamber increases, sensitivity and single to noise ratio (SNR) of the MEMS microphone increase.
Meanwhile, FIG. 2 shows a MEMS microphone 102 in which sound holes 140 are formed in a PCB 110, not in a case 150. No via hole is formed in the case 150. External sound is introduced via the sound holes 140. In this case, the back chamber is a space 151 inside the case, not a space inside a MEMS chip.
Since the back chamber is the space 151 inside the case 150 in the MEMS microphone 102 shown in FIG. 2, a sufficient space for the back chamber is secured. However, in the case of the MEMS microphone 100 shown in FIG. 1, since the back chamber is the inner-MEMS space 126, a space for the back chamber is too narrow and thus insufficient.
If the size of the back chamber is too narrow as shown in FIG. 1, the sound quality of a MEMS microphone is deteriorated due to a small SNR and poor sensitivity.